dilution dilemma
February 7, 2009 12:23 PM Subscribe
A simple chemical concentration / dilution problem.
I am preparing a mixture that requires 2 ounces of 1% Ammonium Hydroxide (NH40H) to be added to 32 ounces of water. All I got is 2% Ammonium Hydroxide. How much water do I use?
I am preparing a mixture that requires 2 ounces of 1% Ammonium Hydroxide (NH40H) to be added to 32 ounces of water. All I got is 2% Ammonium Hydroxide. How much water do I use?
Think of it this way:
If the recipe called for 2 ounces of 1% NH4OH, then you would be adding 0.02 ounces of NH4OH. (2 ounces*.01 concentration = 0.02)
How many ounces of 2% NH4OH does it take to get 0.02 ounces? 0.02 ounces / 0.02 concentration = 1 ounce
posted by chrisamiller at 1:21 PM on February 7, 2009
If the recipe called for 2 ounces of 1% NH4OH, then you would be adding 0.02 ounces of NH4OH. (2 ounces*.01 concentration = 0.02)
How many ounces of 2% NH4OH does it take to get 0.02 ounces? 0.02 ounces / 0.02 concentration = 1 ounce
posted by chrisamiller at 1:21 PM on February 7, 2009
Kid C's will work, but only if you also reduce the quantity of 2% NH4Cl from 2 ounces to 1 ounce.
Another way to look at it: Take 1 ounce of the 2% NH4Cl, add it to 1 ounce water. Now you have 2 ounces of 1% NH4Cl solution.
Add that to the 32 ounces water, you get the mixture you want.
posted by buzzv at 1:23 PM on February 7, 2009
Another way to look at it: Take 1 ounce of the 2% NH4Cl, add it to 1 ounce water. Now you have 2 ounces of 1% NH4Cl solution.
Add that to the 32 ounces water, you get the mixture you want.
posted by buzzv at 1:23 PM on February 7, 2009
Similar adjustment required for chrisamiller's which arrives at 33 ounces of solution -- according to your recipe, you're supposed to end up with a total of 34 ounces of solution. So his method would also need 1 ounce of water added to the final mix.
posted by buzzv at 1:27 PM on February 7, 2009
posted by buzzv at 1:27 PM on February 7, 2009
OOPS -- Re-read Kid Charlemagne's -- his "One ounce" was referring to the NH4Cl, so his is right on. Sorry for the ignorant dis.
posted by buzzv at 1:29 PM on February 7, 2009
posted by buzzv at 1:29 PM on February 7, 2009
Percentages of the sort you quote are usually by weight. If the oz. you are talking about are also ounces of weight, Kid Charlemagne is correct.
But if you are talking fluid ounces, as the "32 ounces of water" leads me to suspect you may be, the situation is a bit stickier.
To appreciate this intuitively, imagine that ammonium hydroxide is so lightweight and expansive that a 1% solution of it is only 10% as dense as pure water. Then 2 fluid ounces of 1% NH4OH would contain only approximately one fifth as much water as 1 fl. oz. of 2% solution added to 1 fl. oz. of pure water. In other words, adding 1 fl. oz. of water to a 2% solution would not give you anything like the 1% solution which is your goal.
If you are talking fluid ounces, adding one ounce of your 2% solution to 33 oz. of pure water will give you exactly what you want only if the density of a 2% solution is exactly the same as the density of pure water, and so is a 1% solution.
In actuality I think they're pretty close, so if you follow the Kid's advice you're good for all practical purposes-- but your theory is a little off.
posted by jamjam at 4:21 PM on February 7, 2009
But if you are talking fluid ounces, as the "32 ounces of water" leads me to suspect you may be, the situation is a bit stickier.
To appreciate this intuitively, imagine that ammonium hydroxide is so lightweight and expansive that a 1% solution of it is only 10% as dense as pure water. Then 2 fluid ounces of 1% NH4OH would contain only approximately one fifth as much water as 1 fl. oz. of 2% solution added to 1 fl. oz. of pure water. In other words, adding 1 fl. oz. of water to a 2% solution would not give you anything like the 1% solution which is your goal.
If you are talking fluid ounces, adding one ounce of your 2% solution to 33 oz. of pure water will give you exactly what you want only if the density of a 2% solution is exactly the same as the density of pure water, and so is a 1% solution.
In actuality I think they're pretty close, so if you follow the Kid's advice you're good for all practical purposes-- but your theory is a little off.
posted by jamjam at 4:21 PM on February 7, 2009
Response by poster: thanks everybody. so okay, i found this table that says 29% conc. Ammonium Hydroxide has density 0.9 grams / mL (versus 1 for water).
does this help?
posted by whiterussian at 9:27 PM on February 7, 2009
does this help?
posted by whiterussian at 9:27 PM on February 7, 2009
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posted by Kid Charlemagne at 12:29 PM on February 7, 2009